In October of 2007, Marvel declared it "Zombie Month" and decided to throw in some variants of the non-zombie titles of the characters as zombies. And yeah, it's pretty much all about being "collector's items". Marvel Zombies were all the rage back then, so you can expect that they milked every drop dry from their cash cow. I think they made five variant covers for the hardcover. I can understand getting the same issue a couple of times from a collector's standpoint, but a 20$ hardcover? Seriously?
I just really don't see the appeal of it anymore, and this is coming from a fan of zombies.